Paliperidone, 3-[2-[4-(6-fluorobenzo[d]isoxazol-3-yl)-1-piperidyl]ethyl]-7-hydroxy-4-methyl-1,5-diazabicyclo[4.4.0]deca-3,5-dien-2-one, is a 5-HT antagonist belonging to the chemical class of benzisoxazole derivatives and a racemic mixture having the following structural formula:

Paliperidone is a metabolite of Risperidone. Marketed under the name, Invega®, Paliperidone is a psychotropic agent approved in the United States for the treatment of schizophrenia.
A process for the synthesis of Paliperidone, is described in U.S. Pat. No. 5,158,952 according to the following scheme.

The preparation of paliperidone via the intermediate 3-(2-chloroethyl)-6,7,8,9-tetrahydro-9-hydroxy-2-methyl-4H-pyrido[1,2-a]-pyrimidin-4-one (CMHTP) is depicted in the last step of the above scheme. This process is performed in the presence of an organic base.
A process for the synthesis of CMHTP is described also in U.S. Pat. No. 5,688,799.
The processes described in the above publications are long, and result in low chemical yields, making their application in the industry very hard. There is a need in the art for a new process for preparing Paliperidone and its intermediates.